(i) Field of the Invention
The present invention relates to a helical guide apparatus usable for a gear shaper and more particularly to a helical guide apparatus of the type which is so constructed that a helical angle to be determined for workpieces can be adjusted steplessly.
(ii) Prior Art Statement
A conventional helical guide apparatus usable for a gear shaper is typically illustrated in FIG. 11 which is a sectional side view of the apparatus. The latter includes a main spindle 2 with a cutter 1 fixedly attached thereto and the main spindle 2 is supported by means of a bearing 3 in such a manner as to reciprocably move in the axial direction and rotate in the circumferential direction. As a crank mechanism is driven, the main spindle 2 is reciprocably displaced in the axial direction via a connecting rod 4 and a spherical bearing 5. FIG. 12 is a perspective view of a male pattern 6 which is firmly fitted onto the upper tapered part of the main spindle 1. Further, the apparatus includes a female pattern 8 which is fitted into a flange 7 in order to guide movement of the male pattern 6. By virtue of the arrangement made in that way it is assured that the main spindle 2 is caused to carry out reciprocable rotational movement as it is reciprocably displaced in the axial direction. During gear cutting operation the flange 7 is rotated by means of a combination of a worm wheel 9 and a worm which is not shown in the drawing while it is maintained in the synchronized state relative to a helical gear which is subjected to gear cutting as a workpiece.
FIGS. 13 and 14 are a schematic view respectively which illustrate a relation between dimensions of the cutter and lead of the helical guide apparatus. As will be apparatus from the drawings, the relation between lead L of the helical guide apparatus and pitch circle diameter d.sub.cp will be represented by the following formulas. EQU L tan .phi.=.pi..multidot.d.sub.cp ( 1) EQU d.sub.cp =(m.sub.II .multidot.Z)/cos .phi. (2)
where .phi. is a helix angle of the cutter l, m.sub.n is a gear tooth module of the cutter l as measured at a right angle relative to gear tooth and Z is a number of gear teeth on the cutter l.
As taught by the formulas, a helix angle which is employable for a single helical guide is restricted only to the case where operative conditions that d.sub.cp is dimensioned within a predetermined range and Z is an integral number are fulfilled. For that reason a cutter which can be practically used with the same lead for the purpose of gear cutting is restricted only to gears having specific dimensions and a helical angle on a helical gear to be worked cannot be changed as required.
Since the conventional helical guide apparatus is constructed in the above-described manner, it is impossible to change a helical angle prior to gear cutting operation for a helical gear unless the male pattern 6 and the female pattern 8 are replaced with other ones. Accordingly, the conventional helical guide apparatus has drawbacks in that designing is limited only within a certain range and it takes a very long time until preparative work prior to gear cutting and replacement of the existent patterns is completed.